Coagulation is the actual formation of a blood clot. It results from a chemical “cascade” which begins with the prothrombin activators released by platelets. Sometimes referred to as “platelet thromboplastin”, these chemicals cause the macromolecule prothrombin to break down into smaller units including thrombin. Thrombin acts on fibrinogen, a soluble polymer present in the plasma, and breaks it into monomers which re-polimerize into insoluble fibrin. The fibrin forms threads which knit the platelets and other cells into the clot.